The present invention relates broadly to a wire consolidator for an electrode discharge machining (EDM) machine which consolidates expended electrode wire by cutting it into predetermined lengths as it is drawn from the EDM machine.
EDM is a process whereby precision tools, dies, parts, and the like may be produced both quickly and accurately via the erosion of material from a conductive workpiece by a controlled electrical spark from an electrode. Inasmuch as there is no direct physical contact between the workpiece and the electrode and no physical force is exerted on the workpiece, the speed or efficacy of the EDM process is not affected by the hardness of workpiece but only its conductivity. This makes EDM ideal not only for machining hard materials such as hardened steel, carbides, and the like, but also for soft materials such as plastics and the like which might be distorted or damaged by the force exerted by traditional cutting tools.
EDM machines may be classified as either vertical or wirecut types. In both types, one terminal of a power supply is connected to a workpiece and the other terminal is connected to an electrode that generates controlled sparks of electricity to effect the removal of material from the workpiece. The workpiece and the electrode are immersed in a dielectric fluid, typically deionized water or a hydrocarbon, which acts as an electrical insulator until a given voltage differential is applied between the electrode and the workpiece. The electrode and workpiece are separated by a defined gap, and a D.C. voltage is applied therebetween to develop an electrical field across the gap. When the breakdown voltage of the dielectric is exceeded, the dielectric is ionized and an electrical current arcs across the gap striking the workpiece and vaporizing material from the surface thereof. As current continues to flow between the electrode and the workpiece, the intense heat developed melts additional material. The current is then pulsed off, the spark is quenched, and dielectric fluid flows into the heated zone to cool and solidify the melt and to transport some of the melt from the zone in the form of small chips or cinders. This cycle is repeated at frequencies of from about 500 to 1,000,000 pulses per second to effect formation of a cavity in the workpiece having a shape mirroring that of the electrode. A small portion of the melted material is redeposited onto the workpiece. However, this recast layer, as it is called, can be minimized by carefully controlling the pulsing of the current and the flow of the dielectric into the heated zone. Other than redeposits, EDM is a completely burr-free machining method.
The conventional or vertical EDM apparatus employs an electrode which is moved towards the workpiece. In contrast, the wirecut EDM variant employs a constantly moving wire as the electrode. Wirecut EDM is especially efficient because the wire erodes a thin line around the perimeter of the required cut rather than eroding the full volume of the cavity as in conventional EDM's. As in the conventional EDM process, the workpiece is typically mounted on a table with two degrees of freedom, i.e., in the X and Y directions. The wire is then threaded around the machine and through the workpiece material. The side of the wire acts like a bandsaw to cut though the workpiece material. However, in this case, the "tooth" of the saw is the electrical discharge and the "blade" is a wire, typically brass or another copper alloy, which can range in size from about a thousandth on up to twelve thousandths of an inch in diameter. As the wire approaches the workpiece, electrical discharges arc from the wire to effect the removal of material from the workpiece. The movement of the table is often computer controlled and automatically driven in a preprogrammed pattern to produce the desired shape. Once the cutting commences, the motion of the wire continually presents a new electrode to the workpiece and thereby lessens electrode wear. For additional information on EDM in general and wirecut EDM in particular, reference may be had to the following, the disclosures of which are expressly incorporated herein by reference: U.S. Pat. No. 4,463,241 and references cited therein; "Update: Wirecut EDM," EDM Digest, pp. 34-35, May/June 1984; and "Electrical Discharge Machining," TechCommentary, Vol. 3, No. 1, published by the Center for Metals Fabrication, Battelle Memorial Institute, Columbus. Ohio.
Although the wirecut EDM process mitigates the electrode wear associated with conventional or vertical EDM, the continuous motion of the wire electrode results in the consumption of significant quantities of brass wire or the like. For example, a machine shop having as few as three wirecut EDM machines may typically use 500 pounds or more of electrode wire each and every month. Handling the expended wire has heretofore presented a problem for such shops. That is, the wirecut EDM machines known in the art generally employ a pair of rollers or the like to teed the expended electrode wire into a container, receptacle, or the like. The randomly fed wire, however, ultimately tangles into a large ball necessitating the frequent emptying of the receptacle. In addition, the ball of tangled wire is seen as waste or scrap product which must be disposed of or salvaged for only a nominal value. Moreover, the expended wire as it is drawn from the machine requires constant attention to keep it from contacting the machine and causing a short circuit or from backing up and jamming or otherwise interfering with the drawing of the wire through the workpiece. Accordingly, it may be seen that improvements in wire handling capabilities would be well-received by the various industries such as tool and die, automotive, aerospace, medical, and the like which employ wirecut EDM processing.
Broad Statement of the Invention
The present invention is addressed to an apparatus for use in a wirecut EDM machine which is adapted for consolidating expended electrode wire by cutting it into predetermined lengths. By delivering the expended electrode wire into a receptacle or the like in a consolidated form, the present invention facilitates the handling of the wire in packing it more efficiently into the receptacle and in militating against roller jams, short circuits, and the like caused by the expended wire backing up and jamming or otherwise contacting the EDM machine. Moreover, the consolidated wire may be marketed as a processed material for use as a reinforcement, electromagnetic shielding, or the like commanding a market price appreciably higher than the salvage value of used electrode wire.
It is, therefore, a feature of the present invention to provide in a wirecut EDM machine having an advancing electrode wire, a wire driver assembly for advancing the electrode wire, and a roller assembly for drawing expended electrode wire from the EDM machine, an apparatus for consolidating the expended wire by cutting it into predetermined lengths as it is drawn from the machine. For cutting the expended wire, a wire shearing assembly having at least one shear tip movable along a predetermined locus is provided. The wire shearing assembly is actuable by a drive means to move the shear tip at a rate effective to cut the expended wire into predetermined lengths. A guide bushing having a guide opening extending therethrough is interposed between the roller assembly of the EDM machine and the wire shearing assembly to receive the expended wire from the roller assembly and to locate it within the locus for shearing impact with the shear tip.
It is also a feature of the invention to provide in a wirecut EDM machine an apparatus for consolidating expended wire which effects the cutting thereof into predetermined lengths without short circuiting the wire. For cutting the expended wire, a wire shearing assembly having at least one shear tip movable along a predetermined locus is provided. The wire shearing assembly is actuable by a drive means to move the shear tip at a rate effective to cut the expended wire into predetermined lengths. A guide bushing having a guide opening extending therethrough is interposed between the roller assembly of the EDM machine and the wire shearing assembly to receive the expended wire from the roller assembly and to locate it within the locus for shearing impact with the shear tip. To electrically insulate the apparatus from the EDM machine, a platform is interposed between the wire shearing assembly and the machine. The platform is configured to suspend the wire shearing assembly therefrom and is formed of a material which is electrically nonconductive. Support means fastenable to the housing and the EDM machine are provided for attaching the apparatus to the EDM machine.
It is also a feature of the invention to provide in a wirecut EDM machine an apparatus for cutting expended electrode wire. The apparatus includes a wire shearing assembly having at least one shear tip movable along a predetermined locus and a cutter having a peripheral portion for supporting the shear tip. The cutter is rotatable about a drive axis by a drive means to define the locus as a circle and to move the shear tip at a rate effective for sheafing the wire into predetermined lengths. A guide bushing having a guide opening extending therethrough is interposed between the roller assembly of the EDM machine and the wire shearing assembly to receive the expended wire from the roller assembly and to locate it within the locus for sheafing impact with the shear tip. To electrically insulate the apparatus from the EDM machine, a platform is interposed between the wire sheafing assembly and the machine. The platform is configured to suspend the wire sheafing assembly therefrom and is formed of a material which is electrically nonconductive. Support means fastenable to the housing and the EDM machine are provided for attaching the apparatus to the machine.
The invention, accordingly, comprises the apparatus possessing the construction, combination of elements, and arrangement of parts which are exemplified in the following detailed disclosure.
For a fuller understanding of the nature and objects of the invention, reference should be had to the following detailed description taken in connection with the accompanying drawings.